Elevator control system



Aug. 16, 1932- R. P. HIGBEE ELEVATOR CONTROL SYSTEM Filed May 19 INVENTOR 1905 fi/gbee.

ATTORNEY Patented A 16, 1932 UNITED STATES raraur OFFICE RAY 1'. menu, m.- rmnaimmam, rannsrLvam'a, 18mm: 10 wasrmcnousn PENNSYLVANIA.

Application filed m 19, ms. Serial Io. 27am.

The invention relates generally to control systems for motors and more particularly to control systems for motors utilized in connection with elevators, hoists and the like.

5 The object ,of the invention, generally stated, is to provide a simple and inexpensive control system for constant-potential elevator systems which shall maintain an elevator-operating characteristic closely approximating that 'of a variable-voltage system.

A more specific object of the invention is to provide a control system for constantpotential elevator systems wherein the effectiveness of the elevator-motor windings is gradually and continuously varied in accordance with the speed of the motor to provide for smooth and rapid acceleration and deceleration of the elevator.

Another object of the invention is to pro vide a two-speed elevator-control system wherein the effectiveness of the high-speed motor winding is gradually and continuousl varied to accelerate the elevator to full speed, and theefiectiveness of the lowspeed winding gradually and continuously varied to decelerate the elevator from hi h. speed to a lower speed as determined by t e low-s eed motor win ing.

A urther object of the invention is to provide for starting an elevator motor at reduced voltage and automatically increasing the voltage impressed upon the motor, in a gradual and continuous manner, to obtain smooth and rapid acceleration.

Other objects of the invention will become evident from the following description, taken in conjunction with the drawing, in which- Figure 1 is a diagrammatic view of a twospeed constant-potential elevator-control system arranged in accordance with the present invention, and- Fig. 2 is a graphical representation of the and deceleration which may be obtained by utilizing the present invention.

Referring to Fi 1 of the drawing, the control system, asown, is suitable for operating a single elevator. As ill rated,

elevator speed-time curves of acceleration of which wlll be the elevator system com risesan elevator car C suspended in a hate way by means of a cable Ca which passes over a drum D to a suitable counterweight C'w, in the usual manner.

The elevator drum D may be driven by a motor of any suitable type. However, in this particular embodiment of the invention, a two-speed alternating-current elevator motor EM is provided. As shown, the motor EM is direct-connected to the drum shaft and is provided with a squirrel-cage rotor R and a double stator winding. The stator is wound with two separate windings having different numbers of poles in any desired ratio, for obtaining high and lowspeed operation. Hereinafter, the lowspeed stator winding will be desi ated as LSW and the high-speed stator winding as HSW. The elevator motor EM is controlled, in the usual mannerfthrou h the agency of a car switch CS on the car which 1s disposed to control the operation of the up and down directional switches .desi nated as 1 and 2, respectively, speed switc es 4 .and 5 and a transfer switch 6.

The elevator motor EM may be supplied with power from any suitable source, and, as shown, a constant-potential source of power, comprising line conductors L1, L2 and L3, is provided.

Since it is necessary to vary the voltage supplied to the motor for obtaining desirable accelerating and decelerating operating characteristics'of the elevator, a lurality of auto transformers 7, 8 and 9, an 11, 12 and 13 are interposed between the power source and the low-speed and high-speed stator windings, respectively. It will be observed that the transformers are provided with transformer windings 14 to 19, inclusive, which are connected to the stator winding of the elevator motor EM in accordance with the well-known auto-transformer principle. 96

'The transformer cores, designated as 21 to 26, inclusive, are also provided with auxiliary windin 27 to 32, inclusive, the purpose described in detail hereinafter.

It will be observed that the transformer win dingsare provided with low-voltage taps at points 33 to 38, inclusive, which are connected to each stator winding through conductor leads 41, 42, or 43 for the low-speed connection, and through conductor leads 44, 45 and 46 for the high-speed connection.

In order that a more comprehensive understanding of the invention may be obtained, a detailed description of the operation of the system will now be given.

Under normal conditions, the motor EM is o erated on the high speed windings, acce eration to full speed bein initiated by movement of the car switch S directly to the extreme position. If desired, however, the motor EM may be operated on the slow speed windin continuously, acceleration to low speed beln initiated by movement of the car switch S to an intermediate s ed position. In the following description, 0th of the above noted control operations will be described in detail.

Assuming that the elevator car C is at a lower floor and that it is desired to operate the elevator at a slow s eed in an u direction, the car switch C first forward position, thereby bridging the fixed contact fingers 47, 48 and 49 by the movable contact se ment 51. In this event, an operating circuit is established for the up directional switch 1 which may be traced from the line conductor L1, through conductor 52, contact fingers 47, 48 and'49, bridged by the movable segment 51, conductor 53, operating coil of switch 1 and conductor 54, to the energized conductor 55, which is connected to the line conductor L2. It will be observed that the conductor 55 is one which is common to all of the switchoperatin circuits and is energized at all times. herefore, in the description which will appear hereinafter, it will be referred to always as the energized conductor 55.

At this time, an operating circuit is also established for the speed switch 5 which extends from the line conductor L1, through conductor 52, fixed contact members 47 and 48, bridged by the segment 51, conductors 56 and 57, the normally closed contact members 58 of the transfer switch 6, conductor 59, and operating coil of the switch 5, to the energized conductor 55.

Upon the closure of the up directional switch 1 and the speed'switch 5, an energizing circuit for the low-speed winding LSW of the elevator motor EM is established. The first phase of the three-phase circuit thus established extends from the line conductor L1, through conductor 61, contact member a of the up direction switch 1, conductors 62 and 63, contact member a of the speed switch 5, winding 15 of transformer 8, tap 34, and conductor 42 to one phase winding is actuate to the mum, and, b

of the low-speed stator windin LSW. A second phase extends from the ine conductor L2, through conductors 55, 64, and 65, contact members 6 of the speed switch 5, winding 14 of the transformer 7, tap 33, and conductor 43 to a second phase of the low-speed stator winding LSW; and the third-phase circuit extends from the line conductor L3, through conductor 66, contact members b of the up directional switch 1, conductors 67 and 68, winding 16 of transformer 9, tap 35 and conductors 41, to a third-phase winding of the low-speed stator winding LSW, thus completing the threephase energizing circuit for the low-speed connection.

It will be observed that the opposite ends of the transformer windings 14, 15 and 16 are disposed to be connected at a common point b means of the switch 71, through the con uctors 72, 73 and 74, which causes the transformers 7, 8 and 9 to provide a low voltage by reason of the tap connections at points 33, 34 and 35 on the respective windings. However, in this instance, the switch 71 is in the open position, and, therefore, the transformer windings 14, 15 and 16 are not connected at the common point and function merely as reactor coils in circuit with the motor windings.

In order to control the efl'ect of the reactor coils upon the voltage applied to the motor windings, a direct-current generator 75 is utilized for excitin the auxiliary windings 27, 28 and 29 of t e transformers 7, 8 and 9, and also the auxiliary windings 30, 31 and 32 of the transformers 11, 12 and 13. It will be understood that, by varying the magnetization of the transformer cores, the effect of the reactor coils will be varied in such manner as to cause a greater or lesser voltage drop across them and thereby var the voltage impressed upon the motor win ings. When a low degree of magnetization is maintained in the cores, the effect of the reactor coils is a maximum, and, therefore, the voltage applied to the motor windings is a miniadually increasing the magnetization o t e cores from a mmimum to a maximum degree, the effect of the reactor coils is gradually and continuously reduced to a minimum, and the voltage applied to the motor windings is a maximum.

In order to control the magnetization of the cores in this manner, the direct-current generator 75 is disposed to be driven by the elevator motor EM. However, in this instance, in order to simplify the drawing, the two machines have been shown separately although it is to be understood that, in operation, they are to be connected together in any suitable manner.

It will be observed that, upon closure of the directional switch 1 and speed switch 5, an energizing circuit for the transformer auxiliary windings was established which may be traced from one terminal of the armature 7 6 of the generator 75, through conductors 77 and 78, auxiliary coils 29, 28 and 5 27, conductor 79, contact member-'0 of the speed switch 5, conductors 81 82 and'83, contact member of the up direction switch land the field winding 84 of the generator 75, to the opposite terminal of the armature 76. Since the speed of the generator 75 varies in accordance with the increasing speed of the elevator motor EM, the generated voltage also increases in direct proortion. The magnetization of the trans ormer cores, therefore, may be so controlled as to gradually decrease the effect of the reactor coils com rising the transformer windings 14, 15 an 16 until a point of maximum magnetic saturation is reached in which case the effect of the reactor coils is reduced to any desired extent.

As will be more fully described hereinafter, in connection with the control operations involved in decelerating the motor EM, it is desirable that, when motor EM is running at the speed determined by the low speed windings, the cores 21, 22 and 23 will be substantially unsaturated, so that the voltage drop across the windings 14, 15 and 16 will be substantially a maximum. ."For reasons which will be more apparent when discussed in connection with the decelerating operations, it is also desirable that the interphase connections of the transformers 7, 8 and 9 remain interrupted by the contact members of relay 71 except at such times as the motor is decelerating from the speed determined by the high speed windings to a speed somewhat in excess of the s eed determined by the low speed windings. 'lhe cores 21, 22 and 23 are, therefore, so designed as to be unsaturated by a voltage value for generator 75 which corresponds to the low speed of the elevator motor EM. Similarly, the coil of relay 103 is so designed as to be ineffective to complete the circuit of relay 71 at a voltage of enerator 75 which corresponds to a' low s ee of the motor EM.

.If the car switch low speed position, therefore, the interphase connections of transformers7, 8 and 9 remain open, windin 14, 15 and 16 function as reactors, the V0 tage dro across which do not appreciably vary as t e s eed of motor EM increases, by reason 0 the unsaturated condition of cores 21, 22 and 23.

To bring the elevator car to rest from low speed, the car switch CS is returnd to the 'neutral and illustrated position thus deenergizing the direction and spjeed switches 1 and 5. The stem may 'be rought finally to rest under t e influence of the usual magnetic brake (not shown).'

As stated the-elevator may 65 ed and rated on the high-speed wind- S is operated to the also starting HSW by operating the car switch Ca directl to the full forward position. In this case, t e low-speed winding is momentarily connected, as ereinbefore described, but, since the transfer to the hi h-speed winding takes-place immediately, 1t has very little efiect.

When the car switch CS is in the full forward position an additional contact finger 50 is bridged by the movable segment 51 to establish an operating circuit for the transfer switch 6, which may be traced from the line conductor L1, through conductor 52, contact fingers 47 and 49, bridged by the segment 51, conductor 85 and o crating coil of the transfer switch 6, to t e ener 'zed conductor 55. Upon the o eration o the transfer switch 6, the normal y closed contact members 58 are opened to deenergize the operating circuit of the speed switch 5, and the normally open contact members are closed to establish an operating circuit for the speed switch 4, which may be traced from the line conductor L1 to contact members 47 and 48, bridged by the segment 51, conductors 56 and 57, contact members 86, conductor 87 and operating coil of the speed switch 4, to the energized conductor 55.

Upon. the closure of the speed switch 4, an energizing circuit for the high-speed winding HSW is established, one phase of which may be traced from the energized conductor 55, through conductors 64 and 88, contact members b of the switch 4, winding 19 of the transformer 13, tap 38, and conductor 44, to one phase of the high-s eed stator winding HSW. Since the up irection switch 1 is closed, conductor 62 is energized, and, therefore, a second-phase circuit extends from conductor 62, through contact members a of the switch 4, winding 18 of the transformer 12, tap 37, and conductor 45, to a second phase of the high-speed stator winding. Likewise, the third-phase circuit extends from the energized conductor 68, through the winding 17 of the transformer 11, and conductor 46 to a third phase of the high-speed stator winding.

In order to provide a low initial voltage for starting or accelerating on the high-speed winding, 'a normally closed switch 89 is utilized to connect the opposite ends of the transformer windings 17, 18 and 19 to a common point through conductors 91, 92 and 93. In order to provide for increasing the volta e 1 of the transformer connection thus esta lished to accelerate the motor EM on the highspeed winding HSW, the speed switch 4 is providedwith a dash-pot-controlled switch 94 for controlling the operation of the trans- I former connecting switch 89. As shown, the armature of the switch 94 is connected to the movable member of the switch 4 by means of a coil spring 95 which, as will be readily understood, permits the closure of switch 4 and permits the closure of the switch 94 to be retarded by the operation of the dash-pot 96. Since the timing of the dash-pot operation may be readily regulated in any well-known manner, the time at which the transformer connection, as made bythe switch 89, is interru ted may be varied as desired.

pon the closure of the switch 94, after a predetermined time interval subsequent to the operation of the speed switch 4, an operating circuit is established for the switch 89 which extends from the energized conductor 55, through contact members (1 of the switch 94, operating coil of switch 89 and conductor 61, to the line conductor L. The switch 89, therefore, is actuated to its open position, which opens the transformer connection. Consequently, the transformer windings 17 18 and 19 remain connected in series with the high-speed stator windings HSW to serve as reactor coils, as described hereinbefore in con nected with the acceleration on the low-speed connection.

It will be observed that the direct-current exciting circuit for the auxiliary coils 30, 31

and 32 was established upon the closure of the speed switch 4 during the transfer from the low-speed to high-speed winding. As shown, this energizing circuit now extends from one terminal of the armature 7 6 of the generator 75, through conductors 77 and 78, auxiliary coils 30, 31 and 32, conductor 97, contact members 0 of the switch 4, conductor 82, contact members a of the directional switch 1 and field winding 84, to the opposite terminal of the armature 76. Since the voltage generated b the generator 75 is now built up to a pre etermined value, depending upon the operating speed of the motor EM, when connected to the transformer taps 36,

A 37 and 38, it will be readily understood that the desi n of the auxiliary windings 30, 31 and 32 sliould be such as to cause a minimum magnetization of the transformer cores 24, and 26, and thereby obtain a maximum effect pf the reactor coils when the motor speed is As described hereinbefore, the excitation of the auxiliary windings 30, 31 and 32 is gradually and continuously increased in response to the increase in speed of the elevator motor EM to a degree where a maximum magnetic saturation of the transformer cores is obtained. In this event, the effect of the reactor coils 17, 18 and 19 is decreased to a minimum, and, therefore, approximately full line "oltage is applied to the motor windings. However, in order to supply full voltage to the elevator motor EM, provision is made for short-circuiting the reactor windings at this time. For this purpose, a switch 98 is utilized, and, as shown, is provided with contact'members a, b and a, each of which is connected to short-circuit the reactor coils upon-the closure of the switch 98 and thereby connect the motor EM directly to the line conductors L1, L2 and L3 through the directional switch 1 and speed switch 4.

In order to control the operation of the short-circuiting switch 98, a rela 99 is provided and disposed to be energized by the direct-current generator 75. As shown, the operating circuit, for "the relay 99 extends from the generator 75, through conductors 77 and 101, operating coil of relay 99, conductors 102, and 83, contact member 0 of the up direction switch 1 and field winding 84, to the op osite terminal of the armature 76. As will be readily understood, the operation of the relay 99 may be made to occur in response to any predetermined voltage of the generator 75, and, in this instance, it is set to operate when the speed of the motor EM increases to approximately its maximum speed, with the reactors in the circuit. Upon the closure of the relay 99, the operating circuit for the short-circuiting switch 98 is established to extend from the energized conductor 55, through contact members of relay 99, operating cell of short-circuiting switch 98, to the conductor 63 which is now energized.

Referring now to Fi 2, the acceleration of the elevator motor E is shown diagrammaticall by the curve designated as X. As will be 0 served, the curve X shows the speed of the elevator at any instant from the time of starting to the point of maximum speed in respect to the total time required to reach the maximum speed. At point A on the curve, an initial low voltage from the transformer windings connected as auto-transformers is applied to the high-speed stator windings, and the motor accelerates along the curve, as shown, to point B. At this time, the short-circuiting switch 89 opens to connect the transformer windings 17, 18 and 19 in the motor circuit to operate as reactors, and acceleration of the motor EM is con-' tinued at, a higher rate to point C with increasing magnetization of the transformer cores, where, in response to the speed of the motor, the switch 98 is operated to shortcircuit the reactor coils, and the acceleration continues, at a lesser rate, to the point of maximum speed at-D.

In reducing the speed of the car preparatory to bringing the elevator to a stop, a sequence of operations occurs which are as follows: the car switch CS is returned to the first forward position, thereby unbridging the contact member which permits the transfer relay 6 to drop out and deenergize the operating coil of the speed switch 4 and, at the same time, establish an energizing circuit for the speed switch 5 through its contact members 58, as described in detail hereinbefore. As will be readily understood, this operation reconnects the motor on the lowspeed termined b the'h'i h-speed winding.

winding while running at a speed deexcess of its normal speed, a certain amount of'braking torque will be obtained which will do d, for its magnitude, u on the value of vo tage impressed upon the ow-speed-windin at the time 'of transfer. Inorder to reduce the braking force to a minimum to obtain a smooth deceleration and eliminate any possibility of a bump occurring at the beginning of the deceleration period, it is necessar to make the initial applied volta relative y low. In order to accomplis this purpose, the connecting switch 71 for the transformer windings 14, 15 and 16 is controlled in such'manner as to connect the transformer windings 14, 15 and 16 to provide a reduced voltage at the time of transfer.

In this instance, the operation of the switch 71 is controlled by a relay 103 which is similar to the relay 99 and is disposed to be operated in response to the development of a voltage by the generator 75. As shown, the

operating coil of the relay 103 is connected for energization from conductor 77, through conductor 104, operating coil of relay 103, conductors 105 and 83, through contact member c of the direction switch 1 and field winding 84, to the opposite terminal of the generator 75. Since the relay 103 may be set to operate at any predetermined voltage value, its operation may be so'timed as to permit the connecting switch 71 to drop out and thereby 'connectthe reactor coils comrising the transformer coils 14, 15 and 16 in the motor circuit in response to any predetermined reduction in the speed of the motor EM after transferring from the highspeed to the low-speed winding.

At the beginning of the deceleration period, with the reactor coils 14, 15 and 16, connected in the motor circuit the voltage developed by the generator is amaximum, causing the reactor cores 21, 22 and 23 to be highly magnetized and, therefore, the eflect of the reactor coils upon the-applied voltage is a minimum. Therefore, an appreciable increase in the voltage impressed upon the lowspeed windings LSW occurs which increases the regenerative-braking action and thereby increases the rate of deceleration. As the speed of the motor EM decreases, the effectiveness'of the reactors increases, since the magnetic saturation of the cores decreases,

- and, therefore, the motor is gradually and continuously decelerated to a speed determined by its low-speed winding operating with the reactors comprising transformer windings 14, 15 and 16 in the circuit. At this point, further deceleration is attained by returning the car switch to the OH position,

which disconnects the elevator motor EM from the power source and simultaneously applies a mechanical brake (not shown) in the usual manner. I In order to more clearly describe the de- %e leration action, reference may be had to 1 wifl designates the maximum operating s eed of the elevator and it is at this point t at the 'transferoccurs from the high-speed wind-- ing to the. low-speed winding upon the return of the car switch CSto the first forward position. ,The elevator then decelerates to a point B while connected to the low-voltage taps 33, 34 and 35 of the transformer, therate 2 and to the curve designated as Y. As be observed, the point A. on the curve of deceleration being comparatively low.

At the point B, the reactor circuit is estab-- lished bythe operation of the rela 103, as described" hereinbefore andthe vollzage applied to the winding LSW is increased to substantially a maximum value, by reason of the fact that the cores 21, 22 and 23 are highly saturated, and the reactance of windmgs 14, 15 and 16 is correspondingly low. The rate of deceleration increases perceptibly at this point by reason of the increased braking torque exerted by the motor. As the s eed falls, however, the magnetization of t e cores 21, 22 and 23 is proportionately decreased, which gradually increases the reactance of windings 14, 15 and 16, and consequently decreases thebraking tor ue exerted by the inotor. The variation 1nbraking torque causes the rate of deceleration of decrease gradually between the points B and C. The point C represents the operating speed of the motor as determined by the low speed windings with the reactive effect of windings 21, 22 and 23 at a maximum value. Further deceleration is obtained to the point D, which is zero s d, by application of the brake, as hereinbe ore described.

Thus, it will be apparent that a relatively I 7 simple and inexpensive control system has been provided wherein an inexpensive squirrel-cage induction motor may be utilized for operating an elevator, and operating characteristics obtained which are substantially the same as those obtained by a more expensive variable-voltage system of control.

Furthermore, by utilizing the reactor principle of operation, the acceleration and deceleration of the elevator is automatically obtained in such manner as to obtain" the most desirable rate of speed change in either the upward or the downward operation of the elevator, with a noticeable elimination of bumps, such as would occur if resistor control of the motor should be employed.

The described embodiment of my invention being merely illustrative, I do not desire to be limited to the exact details of the apparatus disclosed except as they are defined in the appended claims.

I claimas my invention: 1 i 1. In a motor control system, in combination, a motor having dual primary windings for obtaining two-speed operation, a source of ower for/the motor, and means for contro ling the speed of the motor comprising means interposed between the primary windg s of the motor and the source of power for varying the voltage applied to either primary winding, said means including variable impedance means and means for reconnecting said variable impedance means as transformers, said voltage varying means being operable in response to the speed of said motor.

2. In a motor control system, in combination, a motor havin high and low-speed windin s, a source of power for the motor, means or connecting the motor windings to the power source, means interposed between.

the motor and power source for controlling the voltage impressed .upon the windings, said -means comprising auto-transformers with means for interrupting the interphase connections thereof, sald autotransformers having auxiliary windings on the core thereof and means for exciting said auxiliary windings in accordance with the speed of the motor to continuously vary the magnetizationof the core and thereby vary the voltage drop across the transformer windings.

3. In a motor control system, in combination, a motor having high and low-speed primary windings, a source of constant-potential power for the motor, directional and s eed switches for connecting the motor to t e power source, means interposed between the primary windings of the motor and the power source for varying the primary voltage during acceleration and deceleration of the motor, said means comprising auto-transformers provided with main transformer windings and auxiliary windings inductively related thereto, means operable in response to the closure of the high-speed switch for causing said auto-transformer windings to function as reactors to accelerate the motor, and means responsive to the speed of the motor for varying th excitation of the auxiliary windings to change the reactance in the circuit and thereby vary the voltage applied to the stator winding.

4. In a motor-control system, in combination, a motor,'a source of power for the motor, means for connecting the motor to the source of power, voltage-varying means interposed between themotor and the power source, said means comprising auto-transformers having interphase connections, and

' provided with main and auxiliary windings,

means to interrupt the interphase connections of said transformers, and means responsive to the speed of the motor for con- .trolling the effect of the transformer main windings, said means being disposed to vary the excitation of the auxiliary windings tog gradually and continuously vary the effect of the main transformer windings to control the voltage impressed upon the motor.

. 5. In an alternating-current motor control system, a motor having windings, circuits ineluding-said windings, a source of power for said motor, starting mechanism for connecting said motor to said source, and means for controlling the acceleration of said motor comprising additional windings, means comprising'time-controlled means for connecting said additional windings in said circuits as transformers, and for thereafter reconnecting said additional windings in said circuits as reactors, and means res onsive to the speed of said motor for gradua ly reducing the ef-' fect of said additional windings.

6. In an alternating-current motor control system, a motor comprising primary windings, a source of voltage for said motor, circuit connections between said source and said windings including starting switches, and means to control the acceleration of said motor comprising additional windings, means adapted to connect said additional windings in said circuits as transformers to provide a reduced starting voltage for said motor and responsive to the operation of said starting switches to reconnect said additional windings in said circuits as reactors, and means controlled by the speed of said motor for decreasing the effect of said additional windings to thereby gradually increase the voltage supplied to said motor.

7. In an alternating-current motor control system, a motor comprising primary windings, a source of voltage for said motor, circuit connections between said source and said windings including starting switches, and means to control the acceleration of said motor comprising additional windings normall interposed in such circuits, means adap ed to connect said additional windings as transformers to provide a reduced starting voltage for said motor, said last named means being rendered effective by operation of said starting switches to reconnect said additional windings in said circuits as reactors, magnetizable cores associated with said additional windings, means responsive to the speed of said motor for saturating said cores to thereby reduce the effect of said additional windings, and additional means responsive to a predetermined speed of said motor for excluding said additional windings from said circuits.

8. In an alternating-current motor control system, a motor having primary windings, a source'of voltage for said motor, circuit connections between said source and said windings including starting switches, and means to control the acceleration of said motor comprising additional windings normally interposed in said circuits, time-controlled means adapted to connect said additional windings in said circuits as transformersto provide a reduced starting voltage for said motor and to thereafter interrupt said transformer connections and render said additional windings effective as reactors, means responsive to the speed of said motor for gradually decreasing the effect of said adness of the low-sp ditional windings, and means responsive to a predetermined speed of said motor for ex-v eluding said additional windings from said circuits.

. 9 In a motor control system, i combination, a motor-having high and low-s ed primary windings, a source of power for the motor, circuit connections between said motor and said source, and means for graduall decelerating from high speed to low spee includin i; means forltransferring the power connections from the high speed winding to the low speed windings, variable impedance means forg'raduall varying the effectivewinding, and means for reconnecting said variable impedance means as transformers.

19. In a motor control system, in combinat-1on,-a motor, said motor havinghigh and the effectiveness of said low-speed winding in response to a predetermined reduction in motor speed during the initial portion of the deceleration period, and means for gradually and continuously decreasing the efi'ec-- tiveness of the low-speed windingduring the latter portion of the deceleration period to reduce .the motor speed to a value substantially the same as the synchronous speed of the low-speed winding. I

11. In an alternating-current motor control system, a motor having a winding, a source of power for said motor, switching mechanism operable to cause said motor to decelerate between predetermined speed limits, and means associated with said winding to control the rate of change of speed of said motor comprising means, responsive to operation of said switching mechanism, effective to establish an initial low value of braking torque andto thereafter'increase said value of braking torque, and additional means rendered effective after said increase to thereafter gradually reduce the value of said braking torque.

12. In a motor control system, in combination, a motor having high and low-speed pri mary windings,'a source of constant-potential power for the motor, directional and speed switches for connectingthe motor to the power source, means interposed between the primary windings of the motor and the.

power source for varyin the primary voltage during acceleration an deceleration of the motor, said means comprising auto-transof the motor for connecting the main windings of the auto-transformers in the low-speed fprlmary circuit to operate as auto-transformers, said means being disposed to connect said windings as reactors at a predetermined speedafter changing from the highspeed connection to the low-speed connection, and means responsive to the motor speed for privarying the excitation of the auxiliary windings to gradually increase thev reactance value of the reactors, thereby providing smooth deceleration of the elevator from maximum to minimum s ed.

13. In an alternating-current motor-com trol system, a motor having primary winding connections for low and high speed operation of said motor, a source of voltage forsaid -windings, circuit connections between said source and said windings, and selective switching means to control the speed of said motor, means rendered effective by the operation of said switching means to cause deceleration of said motor from high speed to low speed to reduce the voltage supplied to said low speed winding connections, including means for thereafter increasing said voltage, and means operably responsive to the operation of said voltage increasing means for thereafter gradually decreasing said voltage.

14. In .an alternating-current motor control system, a motor having primary winding connections for low and high speed operation, a source of .voltage for said motor, selective switches to control the speed of said motor, and means responsive to operation of said selective switches to cause said motor to decelerate from high speed to low. speed for controlling the rate of change of speed of said motor, said rate-controlling means comprising additional windings, and means disposed to connect said additional windings as transformers in said low speed winding connections to thereby supply an initial reduced voltage to said motor, said means being effective to thereafter interrupt said transformer connections to thereby increase the voltage applied to said motor.

15. In an alternating-current motor control system. a motor having primary winding connections for low and highspecd operation, a source of voltage for said motor, selective switches to control the speed of said motor, and means responsive to operation of said selective switches to cause said motor to controlling the rate of change ofspeed of said motor, said rate-controlling means comprise ing additional windings, means disposed to connect said additional windin s as trans- -formers in said low speed winding connections to thereby supply an initial reduced voltage to said motor, said means bein effective to thereafter'interrupt said trans ormer connections to thereby increase the voltage applied to said motor, and means responsive to the speed of said motor for controlling said interrupting means.

16. In an alternating-current motor con trol system, a motor having primary winding connections for low and high speed operation, a source of voltage for said motor. selective switches to control the speed of said motor, and means responsive to operation of said from hi h speed to low speed for controlling the rate of change of speed of said motor comprisin means to reduce the voltage initially supp ied to said low speed windin connections, means responsive to a pre termined speed of said motor for increasing said voltage, and means res onsive to the s ed of said motor for therea r gradually ecreasing said voltage.

In testimony whereof, I have hereunto sub I scribed my name this 12th day of May 1928.

RAY P. HIGBEE.

selective switches to cause said motor to decelerate from'high speed to low speed for controlling the rate of change of speed of said 'motor. said rate-controlling means comprising additional windings, -means disposed to connect said additional windings as transformers in said low speed winding connections to thereby supply an initial reduced voltage to said motor, and to thereafter render said additional windings effective as reactors and increase the voltage applied to said motor, and means for gradually increasing the effect of said additional windings to thereby reduce the voltage applied to'said motor.

17. In an alternating-current motor control system, a motor having primary winding connections for low and high speed operation, a source of voltage for said "motor, circuitconnections between said source'and said windings, selective switches to control the speed of said motor, means responsive to operation of said selectiveswitches to cause saidmotor to decelerate from high speed to low speed fof'controlling the rate of change of speed of said motor. said rate-controlling means comprising additional windings, means disposed to connect said additional windings as transformers in said low speed winding connections to thereby supply an initial reduced voltage to said motor, and to thereafter render said additional windings eifective as reactors and increase the voltage applied to said motor, means for thereafter gradually increasing the effect of said additional windings to thereby reduce the voltage applied to said motor, and means responsive to the speed of said motor for. controlling said rate-controlling means.

18. In an alternating-current motor-control system, a motor having primary winding connections for low and high'speed operation of said motor, a source of voltage for said motor, circuit connections between said source and said windings, selective switches to control the speed of said motor, and means responsive to operation of said selective swltches to cause said motor to decelerate 

